Production of ethanol from agricultural products using yeast is one of the most important and best-known industrial fermentations. This fermentation is of immense importance to brewers and distillers, bakers and chemical manufacturers. Several processes for the manufacture of fuel-grade ethanol from molasses, corn, grain sorghum and wheat are well known.
Corn is the most popular grain used commercially to manufacture fuel alcohol. The process typically involves a two-stage enzymic conversion of starch to sugar, followed by fermentation and then a distillation to recover alcohol and carbon dioxide. Manufacturers typically dry the grain residue and sell the dried product, commonly called "distillers' dried grains," as an animal feed or a component of other animal feed products. The solubles portion of the residue is often dried separately. Many smaller manufacturers dewater the distillers' grains and ship them in wet form to local feed lots or dairy farms. In these situations, the soluble component of the distillers' grains is generally discarded.
At the present time wheat is not an economical choice as a fermentation substrate unless the spent grains and solubles can be sold for a higher price as human food rather than animal feed. Wheat residues are generally higher in protein, lysine, and threonine than corn residues. The process for manufacturing ethanol from wheat is very similar to that of corn.
Utilization of fermentation residues has received little attention beyond use in animal feeds. A major problem with distillers' grain residue is that it possesses a distinct odor and taste which negatively affect acceptability even for use in animal feed. Bookwalter et al., in "Investigation on the Use of Distillers' Grains or Fractions Thereof in Blended Foods for the Foods for Peace Program and Other Food Applications," USDA Agricultural Research Service (1983), report using solvent extraction and neutral water rinses in an attempt to remove oxidized lipid and fermentation by-products to produce a better tasting product. These attempts were unsuccessful. Tsen et al., in "Evaluation of the Quality of Cookies Supplemented With Distillers' Dried Grain Flour," J. Food Science 47(2) 684 (1982), report that the protein quality and nutritive value of the grain residues deteriorates with harsh heat treatments. Others have noted that nutritional value and overall acceptability vary widely among commercial samples, depending upon how they were processed. Prentice et al., in "High Fiber Bread Containing Brewer's Spent Grains," Cereal Chem. 54:1084 (1977), and "High Fiber Cookies Containing Brewer's Spent Grains," Cereal Chem. 55:712 (1978), report experiments using dried brewers' grains as a baking ingredient for human food. In general, the experiments were not successful. Tsen et al. report that product volume, color, and overall acceptability for bread, sugar, spice cookies and brownies produced were significantly less than for similar products containing no distillers' grain residue, even where substitution levels were 15% or less. Only chocolate chip cookies containing 15% dried distillers' grain residues were as acceptable as chocolate chip cookies containing no distillers' grains.